Various types of boom-mounted equipment are used in the construction and demolition industry for manipulating and operating upon objects too large to be dealt with manually or at locations otherwise unreachable. The booms are tractor mounted and remote controlled, and are used for such tools as buckets, backhoes, excavator rakes, grapples, breakers and cutters. The tools are manipulated by hydraulic cylinders attached to the boom.
Some jobs require a gripping claw in association with the tool, so that the claw and tool can grip or clamp material from both sides, rather than just push or scoop the material. The combination of claw and tool makes it considerably easier to reposition material and to pick it up and set it down as needed. For example, claws attached to breakers can easily reposition large boulders for breaking, and claws attached to such items as buckets or backhoes can be used to remove logs or pipe from a site.
Claws of this type must be capable or opening and closing, and in some cases, complete retraction. Accordingly, they are typically attached in one or two ways. In the first way, the claw is pivotally joined to the tool, with a pivoting link further joining the claw to the boom. The claw in this arrangement pivots simultaneously with the tool, although in the opposite direction. As a result, it can only close against the tool when the tool is at a particular angle with respect to the boom. The tool cannot then be manipulated without opening the claw. In the second way, the claw is mounted to pivot independently of the tool, and has its own hydraulic cylinder mounted on the boom for this purpose. The disadvantage of this arrangement is that the hydraulic cylinder is bulky, not readily attached or removed, and exposed such that it is vulnerable to damage. Also if one were to rotate the tool with the object still gripped by the clamp, one would have to rotate the clamp at the same time in synchronous manner, a difficult maneuver. Still further, claws with hydraulic cylinders mounted on the boom cannot be used with many types of equipment with extendable booms.